Nonwoven wiping cloth

ABSTRACT

A launderable nonwoven wiring cloth is formed by bonding, with heat and pressure, an intermingled array of cotton fibers, rayon fibers, and thermoplastic binder fibers, in a set of discrete and spaced-apart quadrilateral areas, the bonded areas forming a modulated diagonal line inclined at an angle of between 30* and 60* to a line normal to the machine direction axis of the fabric.

United States Patent 1 Such et al. 1 June 5, 1973 [54] NONWOVEN WIPING CLOTH Primary Examiner-William A Powell I75] Inventors: John J. Such, Wrentham; Arthur j 'g g R. Olson, Walpole,both of Mass. Atmmey 0 n [731 Assignee: The Kendall Company, Boston,

Mass.

Filed: Dec. 10, 1971 Appl. No.: 206,802

U.S. Cl. ..l61/l23, 156/220, 156/290, 156/553,161/124, 161/148, 161/150,

Int. Cl. ..B32b 3/00 Field of Search ..16l/l22, 123, 124, 161/148, 150, 170; 156/220, 290, 553

References Cited UNITED STATES PATENTS 11/1970 Such et al ..l61/148 and 60 to a line normal to the machine direction axis of the fabric.

3 Claims, 3 Drawing Figures 1 NONWOVEN WIPIN G CLOTH This invention relates to a launderable nonwoven fabric suitable for use as a reusable household or industrial wiping cloth. More particularly it relates to such a fabric which is a blend of bleached cotton fibers, rayon fibers, and thermoplastic binder fibers, in which the thermoplastic binder fibers are unified in a particular pattern as set forth more fully herein below.

Nonwoven fabrics produced for the wiping cloth market are conventionally formed from carded, gametted, or air-laid webs of textile length fibers, bonded by the application of a polymeric binder material in a set of discrete and spaced-apart points. In general, such nonwoven fabrics are soft and absorbent, but suffer from lack of durability, being prone to linting, and from lack of launderability, tending to tear or shred when laundered as in a Bendix washing machine.

One method of overcoming this difficulty is set forth in U.S. Pat. No. 2,880,111, where certain specific'dimensions of the spots of polymeric binder and certain specific spacings between spots, are said to result in a washable fabric.

An alternative method of creating nonwoven fabrics is set forth in U.S. Pat. No. 3,507,943, to the present inventors. In said patent, a process is described in which an unspun and unwoven sheet of intermingled fibers of textile length is passed between a pair of nonmeshing and non-interpentrating rigid rolls rotating in opposite directions, said rolls being engraved in a pattern of lands and grooves. By this process, maximum pressure is exerted on the sheet material in a set of discrete and spaced-apart areas, bounded by areas which have been subjected to less than the maximum pressure. If the sheet of intermingled fibers comprises thermoplastic fibers, such as polypropylene fibers, and if at least one of the rolls is heated sufficiently to cause the thermoplastic fibers to fuse and bond to each other, the result is a bonded nonwoven fabric. By this process it is possible to make spot-bonded nonwoven fabrics, or what may be termed modulated line-bonded fabrics, in which a symmetrical pattern of diagonally intersecting bonding lines runs from right to left and from left to right across the face of the fabric. The lines are said to be modulated in the sense that heavily bonded quadrilateral areas alternate with intermediately bonded quadrilateral areas along the lengths of the two sets of diagonal lines.

When it was attempted to create by this process a nonwoven wiping cloth which would be soft and absorbent yet lint-free in use and durable to laundering and generally capable of standing up under the rough usage to which household and industrial wiping rags are put, however, it was found that the products so made were deficient in strength, and would not withstand laundering. More particularly, it was found that such products, made from carded fibrous webs in which the principal direction of fiber orientation was in the' long or machine direction, lacked crosswise strength and tended to split or tear in the lengthwise direction when used as a wet wiping cloth.

Various attempts were made to strengthen the fabric by over-all saturation with a secondary bonding agent, or by overprinting the primary fabrics with patterns of binder lines to impart crosswise strength. Such efforts, while strengthening the'product su'fficiently to'impart the desired launderability and abrasion resistance,

bonded the fabric to such a degree that it was unpleasantly stiff and firm and lacked the desired absorbency, which should preferably be at least five or six times the fabric weight when the fabric is immersed in water for one minute, drained for one minute, and the percentage of retained water is determined by weighing the saturated sample.

It has now been found that two hitherto unappreciated factors, considered jointly, have a pronounced influence on the launderability and abrasion resistance of products made according to U.S. Pat. No. 3,507,943. The first factor relates to the size, spacing, and orientation of the quadrilateral areas of maximum bonding, where a land on one roll traverses a land on the second roll, as explained more fully below.

Briefly, the process of this invention produces a nonwoven fabric in which a parallel set of diagonally oriented modulated bonding lines, alternating with a set of substantially unbonded fluffy ribs, runs in a single nonintersecting direction across the face of the fabric.

The second factor is that while nonwoven fabrics of viscose rayon blended with a thermoplastic binder fiber, bonded according to U.S. Pat. No. 3,507,943, will usually not survive a single washing in a Bendix washing machine, replacing the rayon fiber fraction with a blend of rayon and bleached absorbent cotton fibers has the dramatic and unexpected effect of greatly increasing the durability of the nonwoven fabric, enabling it to survive up to four or five launderings in a Bendix washing machine without disintegration, and leaving the fabric still useful as a wiping cloth.

It is an object of this invention to produce a nonwoven wiping cloth which is durable to laundering.

It is a further object of the invention to produce such a wiping cloth comprising a blend of bleached absorbent cotton fibers, viscose rayon fibers, and thermoplastic binder fibers, in which the binder fibers are activated by heat and pressure in a selected pattern to bond the total fiber content of the fabric into a unitary structure.

Further objects of the invention will appear from the following description and drawings, in which:

FIG. 1 represents a pair of press rolls for forming the particular bonding pattern essential for producing a washable nonwoven fabric.

FIG. 2 is a representation of a section of a nonwoven fabric processed through the rolls of FIG. 1.

FIG. 3 is a stylized representation of the pressure pattern produced by the rolls of FIG. 1.

As explained in U.S. Pat. No. 3,507,943, incorporated herein by reference, the pair of helicallyengraved rolls 10 and 12 are mounted in a calender frame and are provided with backup rolls, journals, and conventional means for applying pressure. One or both rolls may be heated, in order to activate the thermoplastic binder fiber content of the mixed fiber web.

In order for the heavily bonded areas to be arranged in such a configuration that there is no natural line of cleavage in the machine direction of the fabric, it is essential that a straight line drawn across the fabric shall pass through a multiplicity of such heavily bonded areas. For this purpose, and to produce the characteristic laundry-durable pattern of FIG. 2, certain criteria of roll configurations must be met. First, the width of the lands on one of the rolls should be at least twice the land width on the other roll. Second, the helix angle on the roll with the lesser land width shall be different L and pitch P,, where pitch refers to the combined width of a land and a groove i.e., the repetition of a pattern.

The helix angle 13 on the lower roll 12, with land width L and pitch P is less than the helix angle B on the upper roll 10. In general, in order to give the desired durable pattern of FIG. 2, the helix angle of one roll should be between 50 and 75 to the horizontal,

and the helix angle of the other roll should incline between 15 and 45 to the horizontal.

In order to form a launderable nonwoven fabric with a soft hand and at least 500 percent water pickup, it is desirable that the heavily bonded areas, shown as black quadrilaterals in FIG. 3, constitute not over 35 percent of the total area of the fabric. For this purpose, the land width L of the upper roll may be in the vicinity of 0.075 inches, and the pitch P may be about 0.130 inches. With dimensions of this sort, the land width L of the lower roll 12 may be about 0.035 inches, and the pitch interval P, of the lower roll about 0.065 inches. These are to be taken as illustrative and not restrictive figures, the critical point being that the pitch P of the roll 10 be between two and three times the pitch P of the roll 12 with the narrower lands.

In this manner, an autogenously bonded fabric is formed, which is held together by the fusion of the binder fiber content with the rayon and cotton fibers. The fabric is characterized by a set of diagonallyinclined ribs of substantially unbonded mixed fibers, inclined at an angle of between about 30 and about 60 to an axis drawn across the machine direction of the fabric. These ribs, 18 in FIGS. 2 and 3, alternate with a similarly-inclined set of ribs 14, which are modulated bonding lines. By modulated is meant that these lines consist of alternating quadrilateral areas 15 of maxi- .mum compression, where the binder and non-binder fibers are strongly bonded, and similar areas 16 where the degree of inter-fiber bonding is intermediate. Characteristically, the unbonded continuous ribs 18 will appear, in cross-section, at least 8 or 10 times as thick as the strongly-bonded quadrilateral areas 15, and 2 to 3 times as thick as the intermediately-bonded areas 16. This alternating arrangement of bonded and unbonded ribs imparts an exceptional efficiency to the fabric in wiping and cleaning operations.

Following the general calendering procedure set forth in US. Pat. No. 3,507,943, rolls l0 and 12 were heated to 460F. and loaded with a pressure equal to 150 pounds per inch of nip width. Through this nip there was processed a web of intimately blended and intermingled fibers consisting of 20 percent 1.8 denier 19/ 16' inch polypropylene fibers, 50 percent bleached absorbent cotton fibers, and 30 percent 1.5 denier 1 9/16 inch dull crimped rayon fibers.

The resultant fabric is shown schematically in FIG. 2, where the quadrilateral areas 15 represent the crossing of a land of one roll over a land of the other roll, and

,hence represent areas of maximum compaction and futhe heated rolls, but where heat radiating from the land area has effected an intermediate degree of compression and fusion. These intermediate areas 16 of partial bonding, alternating with the highly compressed, fully bonded areas 15, may be considered as creating a modulated line-bond pattern in which lines of unified fibers, 14, run diagonally across the face of the fabric. Each of the lines 14 is contiguous to a lofty rib 18 of substantially uncompacted fibers.

The proportions of the fibers used in producing a launderable wiping cloth may vary, but the presence of a certain amount of cotton does seem to be essential to provide abrasion resistance, while minimizing the formation of fuzz, lint, and broken fibers which are undesirable in a wiping cloth. In part this may be due to the twisted rugose contour of cotton fibers, and their ability to form strong bonds with thermoplastic fibers. In part, also, it may be due to the fact that while the dry strengths of viscose rayon and cotton may be of similar orders of magnitude, in grams per denier, the wet strength of cotton fibers is 1 10 percent to percent of their dry strength, while the wet strength of viscose rayon fibers is between 44 percent and 54 percent of 7 their dry strength. As a general rule, durable and launderable wiping cloths can be made by this process wherein the proportion by weight of viscose rayon fibers lies between 20 percent and 50 percent; the bleached absorbent cotton fibers between 30 percent and 50 percent; and the thermoplastic binder fibers between 15 percent and 30 percent. Various thermoplastic fibers may be used, such as polypropylene, polyvinyl acetate-polyvinyl chloride copolymers, plasticized cellulose acetate, and the like, with polypropylene being the thermoplastic fiber of choice.

Having thus disclosed our invention, we claim:

1. An autogenously bonded launderable nonwoven fabric suitable for use as a wiping cloth which comprises a web of intermingled unspun and unwoven cotton fibers, rayon fibers, and thermoplastic binder fibers,

said binder fibers being strongly bonded to each other and to said rayon fibers and said cotton fibers in spaced-apart sets of quadrilateral areas,

said quadrilateral areas lying in depressed diagonal lines which are inclined at an angle of between about 30 and about 60 to a line normal to the machine direction axis of the fabric,

the length of the longer side of said quadrilateral areas being between 2 and 3 times the shorter side of said areas,

the strongly bonded quadrilateral areas each being bounded on their long sides by similarly-shaped areas in which the binder fibers are less strongly bonded to the rayon and cotton fibers,

the depressed diagonal lines containing the alternating sets of quadrilateral areas alternating in turn with thick ribs of similar inclination,

said ribs being composed of substantially unbonded fibers.

2. The product according to claim 1 in which the viscose rayon fibers constitute between 20 percent and 50 percent by weight of the total fiber content; the cotton fibers between 30 percent and 50 percent; and the binder fibers between 15 percent and 30 percent.

3. The product according to claim 2 wherein the binder fibers are polypropylene fibers. 

2. The product according to claim 1 in which the viscose rayon fibers constitute between 20 percent and 50 percent by weight of the total fiber content; the cotton fibers between 30 percent and 50 percent; and the binder fibers between 15 percent and 30 percent.
 3. The product according to claim 2 wherein the binder fibers are polypropylene fibers. 